Magnesium-base rare earth alloys



MAGNESiUM-BASE RARE EARTH ALLOYS Charles de Itohden, Neuilly-sur-Seine, France;

vested in the Allen Property Custodian No Drawing. Application March 29, 1940, Serial No. 326,724. In France April 21, was

2 Claims.

other minerals rich in the cerium group of rare earths, without any separation of the metallic constituents or alteration in their relative proportions except for a slight increase in the cerium content, the remainder being composed of lanthanum, praseodymium, neodymium and samerium.

Experience has shown that at relatively high temperatures no other ultra-light alloys possess such advantageous mechanical characteristics as the alloys of magnesium with cerium or misch metal. UnfortunateLv such alloys do not develop their full characteristics unless they contain over 2% of cerium or misch metal, and much higher percentages may be needed in order to obtain optimum figures. It will easily be understood therefore that the high initial cost of cerium or misch metal has prevented industrial development of these alloys, which have so far never been placed on the commercial market.

The present invention consists in utilising for magnesium-base alloys, instead of cerium or misch metal, a mixture of lanthanum, neodymium, praseodynium together with a small quantity of Samarium. This mixture of rare earth metals may if desired contain a small amount of cerium, or be almost completely free from the same, but in the event of appreciable quantities of cerium being present, the quantity should not exceed a few per cent of the total quantity of rare earth metals.

The present invention has for its basis the following facts. In the first place, magnesium base alloys with the cerium group of rare earth metals retain their excellent and very peculiar mechanical properties even if the cerium is completely or almost completely absent. In the second place, the inventor has made the surprising discovery that the presence of cerium in substantial amounts has the effect of lowering the resistance to corrosion of these alloys which are so highly interesting from the point oi view of their mechanical characteristics.

taining 9.5% of misch metal, 2% of Mn and 0.4% of Ca shows a remarkable resistance to corrosion, as the following flgures show. Two samples of this alloy, weighing respectively 57.150 grs. and 54.550 grs. were immersed for 48 hours in seawater. Each sample lost 0.580 gr., representing a loss of 1.01% and 1.06% respectively. Two other samples of a similar alloy identical in iorm but in which the 9.5% of rare earth metals was substantially free from cerium, weighing respectively 64.250 grs. and 50.800 grs., were similarly immersed in sea-water for 48 hours. The loss of weight found in each case was 0.400 gr., representing a loss respectively of 0.82% and 0.79%.

As a. further example may be cited a sample of an alloy containing 6% misch metal, 2% Mn and 0.4% Ca. This sample, which weighed 50.800 grs. lost after 30 days immersion in sea-water 5.2% of its weight. Another sample or a similar alloy, identical in form, but in which the 6% of misch metal was substantially free from cerium, lost under identical conditions 2.1% of its weight.

The present invention therefore has for its object and scope ultra light alloys of magnesium To cite a particular instance, an alloy conand rare earth metals substantially ,tree from cerium. The alloys also contain 1 to 2% of manganese and from 0.2% to 1% of calcium,

When one desires to produce an alloy relatively high in rare earth metals, it is generally preferable to prepare separately the alloy containing the rare earth metals free from cerium. This may be done by any appropriate process. Thus for instance the cerium may be initially separated in aqueous solution from the other rare earth metals, these latter being then isolated by electrolysis with a mercury cathode, the resulting amalgam being distilled so as to recover the rare earth metals. Or again the rare earth metals deprived of substantially all their cerium may be transformed into the chlorides which are fused and electrolysed. This method presents considerable advantages if one wishes to prepare alloys containing a high rare earth metal content, since at the normal working temperatures (650-900" 0.)

there is but little diflerence in ailinity tor the halogens between magnesium and the rare earth metals, and since at higher temperatures, where theoretically the reduction of rare earth-compounds by magnesium should prove easier, thismerely by displacing the metals of the rare earths from their halogen compounds, either by magreasonable cost price, this being due to the sepanesium, with simultaneous formation of the desired alloy, or by means of calcium already incorporated in the magnesium or the rare earth metal alloy serving as a starting material.

Thefollowing is a preferred method of executing the said invention, which is however givensolely by way of example, and which must not'be construed in any limitative spirit. Monazite sand is attacked by acid, and the cerium separated as CeO: by any known process. The mixture of rare earth metal compounds, substantially free from cerium, which may be for instance in the form of carbonates, is then converted into chlorides by treatment with hydrochloric acid, and the said chlorides are then dehydrated, fused and electrolysed in aniron crucible with a carbon anode. The resulting misch metal free from cerium is then cast into ingots. The next step is to prepare an alloy with magnesium containing about 25% of rare earth metals, which in turn is used for preparing an alloy of magnesium containing 5% of rare earth metals substantially free from cerium, 1% 01' Mn and 0.2% of Ca, the remainder being Mg. The said alloy is then forged and used for pistons, propeller blades for aeroplanes etc.

The hereinbefore described invention permits of obtaining alloys of desired composition at a ration of the cerium and its utilisation for other purposes. Moreover the resulting alloys of the present invention have an increased resistance tocorrosion.

The hereinbefore described invention also covs ers by way of new industrial products, magnesium-base alloys with rare earth metals substantially free from cerium, and also magnesium alloys containing higher percentages of the said cerium-free rare earth-metals which may serve as a starting point for the production of lower percentage alloys for commercial use.

I claim:

1. A light magnesium alloy having improved resistance to corrosion from sea-water, which contains approximately two per cent of manganese, four-tenths per cent of calcium, from flve to nine percent of a misch metal substantially free of cerium and the remainder magnesium.

2. A light magnesium alloy having improved resistance to corrosion from sea-water, which contains approximately two percent of manganese, four-tenths percent of calcium, from five to nine percent of a mixture of lanthanum, ne- Odymium, praseodymium and samarium, each in substantial amount, and the remainder masnesium.

CHARLES ns ROHDEN. 

